An active matrix type liquid crystal display using a thin film transistor (TFT) is used in various fields such as a display of a camcorder and a display of a personal computer or a personal word processor owing to its advantages such as a reduced thickness, a reduced weight, and capability of low voltage driving, and there is a large market for such liquid crystal display.
In recent years, particularly, the liquid crystal display has been used for displaying dynamic images and has been applied to televisions in addition to the conventional use for displaying static images in a personal computer and the like, and there is an increasing demand for a liquid crystal display device suitable for such dynamic image display. In order to meet such demand, a liquid crystal display element of a bend orientation is proposed in Japanese Unexamined Patent Publication No. 7- 84254 as the liquid crystal element which enables improvements in high speed response required for the dynamic image display. In the liquid crystal element of bend orientation, liquid crystals rapidly change with a change of voltage, thereby realizing the high speed response. It is possible to achieve such bend orientation by transitioning an initial orientation which is called splay orientation through an application of a voltage; however, the bend orientation undesirably returns to the splay orientation when the voltage applied to the liquid crystals is below a predetermined value. In view of the above problem, the present applicant has filed a Japanese patent application (Japanese Patent Application No. 2000- 214827 which has not been published yet) which proposes a driving method of a liquid crystal display element, wherein a signal voltage different from a picture signal voltage is applied to liquid crystals in order to prevent the reverse transition from the bend orientation to the splay orientation.
Also, Japanese Unexamined Patent Publication No. 11 - 109921 proposes a driving method of a liquid crystal display element, wherein a blanking image is displayed using a non-image signal which is inserted between picture signals so as to reduce a blurring of dynamic image which is peculiar to the liquid crystals.
This conventional liquid crystal display element driving method will be explained with reference to the accompanying drawings. Shown in FIG. 12 is a timing chart indicating contents of gate signals and a source signal in the conventional liquid crystal display element driving method, wherein FIG. 12A is a graph showing the gate signals and FIG. 12B is a graph showing the source signal.
In FIGS. 12A and 12B, a gate ON voltage Vgon is applied to gate lines sequentially using gate signals Sgl to Sgend, thereby bringing switching elements provided for respective pixels to an ON state. Then, a source signal Ssn is supplied from each of source lines to each of the pixels in accordance with the switching ON timing, and a potential difference between a pixel electrode and a counter electrode reaches a value responsive to a voltage applied by the source signal Ssn. Hereinafter, a state in which a potential difference between a pixel electrode and a counter electrode in a certain pixel becomes a predetermined voltage by the source signal Ssn is expressed as the source signal is written to the pixel. In this case, the gate ON voltage Vgon is applied twice to each of the gate lines during each of frame periods Po and Pe; a picture signal 101 from the source line is written as the source signal Ssn to each of the pixels in the first Vgon application, and a non-picture signal 102 from the source line is written as the source signal Ssn to each of the pixels in the second Vgon application. Owing to the writing of non-picture signal 102, the reverse transition of liquid crystals to the splay orientation is prevented in each of the pixel.
By the way, in general liquid crystal display devices, a liquid crystal display element is AC driven for the purpose of suppressing burn-in of liquid crystals and generation of display unevenness due to ions. Accordingly, the non-picture signal 102 is written to the pixels when applying the second gate ON voltage Vgon during the odd frame period Po, and then the picture signal 101 having a reverse polarity is written to the pixels when applying the first gate ON voltage Vgon during the succeeding even frame period Pe. Therefore, the writing of the picture signal 101 causes a great potential difference, and the potential of the pixel electrode does not reach the potential responsive to the picture signal 101 to lead to generation of the display unevenness.
Further, along with future developments in high resolution liquid crystal panels, time allowed for writing one source signal will become shorter and shorter, and, therefore, it will be necessary to write a signal with reliability in such shortened period of time.